feat(issue search): query string for boolean operators and phrase search (#6952)

closes #6909

related to forgejo/design#14

# Description

Adds the following boolean operators for issues when using an indexer (with minor caveats)

- `+term`: `term` MUST be present for any result
- `-term`: negation; exclude results that contain `term`
- `"this is a term"`: matches the exact phrase `this is a term`

In all cases the special characters may be escaped by the prefix `\`

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/6952
Reviewed-by: 0ko <0ko@noreply.codeberg.org>
Reviewed-by: Otto <otto@codeberg.org>
Co-authored-by: Shiny Nematoda <snematoda.751k2@aleeas.com>
Co-committed-by: Shiny Nematoda <snematoda.751k2@aleeas.com>

modules/indexer/issues/internal/qstring_test.go

@@ -0,0 +1,171 @@
+// Copyright 2025 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package internal
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+type testIssueQueryStringOpt struct {
+	Keyword string
+	Results []Token
+}
+
+var testOpts = []testIssueQueryStringOpt{
+	{
+		Keyword: "Hello",
+		Results: []Token{
+			{
+				Term:  "Hello",
+				Fuzzy: true,
+				Kind:  BoolOptShould,
+			},
+		},
+	},
+	{
+		Keyword: "Hello World",
+		Results: []Token{
+			{
+				Term:  "Hello",
+				Fuzzy: true,
+				Kind:  BoolOptShould,
+			},
+			{
+				Term:  "World",
+				Fuzzy: true,
+				Kind:  BoolOptShould,
+			},
+		},
+	},
+	{
+		Keyword: "+Hello +World",
+		Results: []Token{
+			{
+				Term:  "Hello",
+				Fuzzy: true,
+				Kind:  BoolOptMust,
+			},
+			{
+				Term:  "World",
+				Fuzzy: true,
+				Kind:  BoolOptMust,
+			},
+		},
+	},
+	{
+		Keyword: "+Hello World",
+		Results: []Token{
+			{
+				Term:  "Hello",
+				Fuzzy: true,
+				Kind:  BoolOptMust,
+			},
+			{
+				Term:  "World",
+				Fuzzy: true,
+				Kind:  BoolOptShould,
+			},
+		},
+	},
+	{
+		Keyword: "+Hello -World",
+		Results: []Token{
+			{
+				Term:  "Hello",
+				Fuzzy: true,
+				Kind:  BoolOptMust,
+			},
+			{
+				Term:  "World",
+				Fuzzy: true,
+				Kind:  BoolOptNot,
+			},
+		},
+	},
+	{
+		Keyword: "\"Hello World\"",
+		Results: []Token{
+			{
+				Term:  "Hello World",
+				Fuzzy: false,
+				Kind:  BoolOptShould,
+			},
+		},
+	},
+	{
+		Keyword: "+\"Hello World\"",
+		Results: []Token{
+			{
+				Term:  "Hello World",
+				Fuzzy: false,
+				Kind:  BoolOptMust,
+			},
+		},
+	},
+	{
+		Keyword: "-\"Hello World\"",
+		Results: []Token{
+			{
+				Term:  "Hello World",
+				Fuzzy: false,
+				Kind:  BoolOptNot,
+			},
+		},
+	},
+	{
+		Keyword: "\"+Hello -World\"",
+		Results: []Token{
+			{
+				Term:  "+Hello -World",
+				Fuzzy: false,
+				Kind:  BoolOptShould,
+			},
+		},
+	},
+	{
+		Keyword: "\\+Hello", // \+Hello => +Hello
+		Results: []Token{
+			{
+				Term:  "+Hello",
+				Fuzzy: true,
+				Kind:  BoolOptShould,
+			},
+		},
+	},
+	{
+		Keyword: "\\\\Hello", // \\Hello => \Hello
+		Results: []Token{
+			{
+				Term:  "\\Hello",
+				Fuzzy: true,
+				Kind:  BoolOptShould,
+			},
+		},
+	},
+	{
+		Keyword: "\\\"Hello", // \"Hello => "Hello
+		Results: []Token{
+			{
+				Term:  "\"Hello",
+				Fuzzy: true,
+				Kind:  BoolOptShould,
+			},
+		},
+	},
+}
+
+func TestIssueQueryString(t *testing.T) {
+	var opt SearchOptions
+	for _, res := range testOpts {
+		t.Run(opt.Keyword, func(t *testing.T) {
+			opt.Keyword = res.Keyword
+			tokens, err := opt.Tokens()
+			require.NoError(t, err)
+			assert.Equal(t, res.Results, tokens)
+		})
+	}
+}